大约有 37,000 项符合查询结果（耗时：0.0234秒） [XML]
Storing time-series data, relational or non?
... clause, it is very fast, and the query does not depend on the size of the table (grabbing 1,000 rows from a 16 billion row table is instantaneous).
Your table has one serious impediment. Given your description, the actual PK is (Device, Metric, DateTime). (Please don't call it TimeStamp, that mea...
Is a view faster than a simple query?
...y referenced by another query as the optimizer will use them in place of a table reference when appropriate.
Again, the documentation:
The indexed view can be used in a query execution in two ways. The query can reference the indexed view directly, or, more importantly, the query optimizer c...
How to understand nil vs. empty vs. blank in Ruby
...
I made this useful table with all the cases:
blank?, present? are provided by Rails.
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How to vertically align into the center of the content of a div with defined width/height?
...I have found you have four options:
Version 1: Parent div with display as table-cell
If you do not mind using the display:table-cell on your parent div, you can use of the following options:
.area{
height: 100px;
width: 100px;
background: red;
margin:10px;
text-align: center;
...
Big-O summary for Java Collections Framework implementations? [closed]
...s next notes
HashSet O(1) O(1) O(h/n) h is the table capacity
LinkedHashSet O(1) O(1) O(1)
CopyOnWriteArraySet O(n) O(n) O(1)
EnumSet O(1) O(1) O(1)
TreeSet O(log n) O(log n) O(log n)
ConcurrentSkipListSet O...
Fastest way to determine if an integer is between two integers (inclusive) with known sets of values
...doing this for a very finite set of values, then you could create a lookup table. Performing the indexing might be more expensive, but if you can fit the entire table in cache, then you can remove all branching from the code, which should speed things up.
For your data the lookup table would be 12...
Equivalent of LIMIT and OFFSET for SQL Server?
... ROW_NUMBER() OVER (ORDER BY SortCol1, SortCol2, ...) AS RowNum
FROM Table
WHERE <whatever>
)
SELECT *
FROM Results_CTE
WHERE RowNum >= @Offset
AND RowNum < @Offset + @Limit
The advantage here is the parameterization of the offset and limit in case you decide to change your p...
'console' is undefined error for Internet Explorer
...le.debug
*
* Chrome 41.0.2272.118: debug,error,info,log,warn,dir,dirxml,table,trace,assert,count,markTimeline,profile,profileEnd,time,timeEnd,timeStamp,timeline,timelineEnd,group,groupCollapsed,groupEnd,clear
* Firefox 37.0.1: log,info,warn,error,exception,debug,table,trace,dir,group,groupCollap...
LIKE vs CONTAINS on SQL Server
...e an index, since it starts with a wildcard, so will always require a full table scan.
The CONTAINS query should be:
SELECT * FROM table WHERE CONTAINS(Column, 'test');
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How to show the last queries executed on MySQL?
...ontrol this option globally at runtime:
Execute SET GLOBAL log_output = 'TABLE';
Execute SET GLOBAL general_log = 'ON';
Take a look at the table mysql.general_log
If you prefer to output to a file instead of a table:
SET GLOBAL log_output = "FILE"; the default.
SET GLOBAL general_log_file = ...